Engines may operate with a variable number of strokes in a combustion cycle. For example, an engine may be configured to operate in a first mode with cylinders carrying out combustion in a two-stroke combustion cycle, and further to operate in a second mode with cylinders carrying out combustion in a two-stroke combustion cycle. The engine may transition, during engine operation, between these modes with various valve systems, such as cam switching actuators, electric cylinder valve actuators, etc.
In one example, the engine may commence combustion with a two-stroke combustion cycle in a cylinder. One such example is described in US 2006-0254550, which describes commencing combustion with a plurality of cylinders having combustion in a commonly aligned stroke, and the increasing/decreasing the number of strokes in a cylinder to return to a desired, sequential, firing order, for example.
The inventors herein have recognized some issues with the above approaches, in that commencing combustion out of the firing order sequence in order to have two cylinders firing at the same time may generate unacceptable noise, vibration, and harshness, especially during engine idle-stop and related re-start conditions.
As such, the above issues may be at least partially addressed by a method of starting an engine, the engine having at least a cylinder and a compression device coupled to an intake of the engine, the method comprising: during engine re-start operation of an engine idle-stop condition, commencing combustion in the cylinder from a non-combusting condition, the combustion in a two-stroke combustion cycle of the cylinder. Such starting may take advantage of the ability of the engine to handle two-stroke combustion in the first combustion event, since residuals from previous combustion are substantially not present, even with insufficient boost (such as when electrically powered boost is unavailable due to low battery state of charge, etc.). Further, such starting can take advantage of an already warmed-up engine present during idle-stop/restart conditions.
However, in some examples, at least partially electrically powered boosting operation may also be used to extend the two-stroke operation during a start, thus further reducing engine starting time and improving vehicle launch from idle-stop operation. Such operation is particularly beneficial since exhaust flow during idle-stop re-starts may be insufficient to generate boost levels that can enable two-stroke operation in a poppet valve engine.
It should be understood that the background and summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.